In the research laboratory, many studies employing cells are conducted using cultured cells that often exhibit logarithmic growth. In nature, however, cells are rarely in a logarithmic growth-rate and often are in a stationary state. This phenomenon is an important consideration in the development of clinical diagnostics for the detection of cells since clinical samples can contain cells that are not in a metabolic state that supports optimal growth. In some cases, cells can be obtained that do not grow under the assay conditions intended to detect the cells. As such, when testing for the presence of cells directly from a clinical or environmental sample, it can oftentimes be important to employ an assay that operates independent of cell growth.
Even when cells are isolated and cultured in the laboratory there can still be situations in which individual strains of isolated cells can exhibit varying growth characteristics. When such cells exhibit sub-optimal growth, this can lead to a cell not being detected by an assay that generally requires growth. Example 9 of WO 2014/145899 exemplifies this situation (See page 80, line 2-page 82, line 33, and FIG. 26B). In that assay, S. aureus cells were monitored for growth in the presence of clindamycin. The assay was intended for distinguishing a clindamycin susceptible vs. resistant phenotype making the determination based on the growth rate of the bacteria in the presence of clindamycin. In the assay, one clindamycin-resistant isolate of bacteria was misinterpreted as clindamycin-sensitive because the isolate exhibited a sub-optimal growth rate.
As such, assays that generally require a minimum amount of growth or a minimum growth rate may not detect target cells that do not exhibit the required growth characteristics during the assay.
Related patent applications include: PCT/US2014/026536, filed on Mar. 13, 2014, which is hereby incorporated by reference, in its entirety, for all purposes.